The present invention relates generally to a superconducting magnet coil support structure. More particularly, the present invention relates to a method and apparatus for supporting a superconducting magnet in a Magnetic Resonance Imager (MRI) System.
Current Magnetic Resonance Imager (MRI) systems include a superconducting magnet that generates a temporally constant primary magnetic field. The superconducting magnet is used in conjunction with a magnetic gradient coil assembly, which is sequentially pulsed to create a sequence of controlled gradients in the static magnetic field during a MRI data gathering sequence. The superconducting magnet and the magnetic gradient coil assembly have a radio frequency (RF) shield disposed therebetween. The controlled sequential gradients are effectuated throughout a patient imaging volume (patient bore), which is coupled to at least one MRI (RF) coil or antennae. The RF coils are located between the magnetic gradient coil assembly and the patient bore.
As a part of a typical MRI, RF signals of suitable frequencies are transmitted into the patient bore. Nuclear magnetic resonance (nMR) responsive RF signals are received from the patient bore via the RF coils. Information encoded within the frequency and phase parameters of the received RF signals, by the use of a RF circuit, is processed to form visual images. These visual images represent the distribution of nMR nuclei within a cross-section or volume of a patient being scanned within the patient bore.
In current MRI systems, the superconducting magnet includes a plurality of superconducting magnet coils. The superconducting magnet is supported by a superconducting magnet coil support structure within a toroidal helium vessel. When the superconducting magnet suddenly quits carrying a charge or current, quench forces result, causing the superconducting magnet coils to move. The superconducting magnet coil support structure maintains the superconducting magnet coils tight and snug as to prevent movement.
In the production of current MRI systems, fiberglass cloth is used to build the superconducting magnet coil support structure. The superconducting magnet coil support structure is formed during a traditional wet winding process. During the traditional wet winding process, fiberglass is applied to and wound around a cylindrical shaped mandrel. The mandrel is large in size to accommodate size of the superconducting magnet coil support structure. The mandrel is typically formed of steel using a machining process in order to form a mandrel that is capable of withstanding pressures and temperatures experienced during formation of the superconducting magnet coil support structure.
Some other techniques of forming a tooling exist, such as stereolithography. Stereolithography techniques and the like are intended for the formation of relatively small components. Equipment utilized within these techniques is currently incapable of forming a tooling large enough to accommodate a superconducting magnet coil support structure. Also, such techniques are simply impractical for the formation of a superconducting magnet coil support structure, since in doing so would result in a large amount of wasted material.
Several layers of standard sized fiber cloth having a standard width are dipped into a liquid epoxy and applied to the mandrel. The fiberglass is allowed to cure to form a superconducting magnet coil support structure having a solid body. The superconducting magnet coil support structure is removed from the mandrel. Pockets are then cut in the exterior side of the superconducting magnet coil support structure to support the superconducting magnet. The dimensions and geometries of the pockets correspond to the dimensions and geometries of the superconducting magnet coils. Spacers remain between pockets in the superconducting magnet coil support structure to fill gaps between adjacent superconducting magnet coils. The closely matching dimensions and geometries allows the superconducting magnet coil support structure to maintain the superconducting magnet tight and snug as to prevent freedom of movement.
Superconducting magnet coils that have non-standard dimensions may require pockets in the superconducting magnet coil support structure, which are deeper and narrower than standard pocket depths and widths. The non-standard dimensions are more difficult to cut out then the standard dimensions. Thus, specialized tooling and equipment is necessary to continue using the traditional wet winding process, increasing time and expense involved therein. Also, in order to efficiently and reliably utilize the specialized tooling and equipment, additional technician training time and expense would be incurred. The difficulty level is sufficient and known to one skilled in the art, to cause the traditional process used to create the superconducting magnet coil support structure having non-standard dimensions to be infeasible and obsolete.
The traditional wet winding process is also unstable, inaccurate, and inefficient for the following reasons. The fiberglass cloth is free to move throughout the wet winding process causing voids and incorrect dimensions of the superconducting magnet coil support structure. These inaccuracies are increased for a superconducting magnet coil support structure having non-standard dimensions. The voids are usually filled with epoxy. Extra time and expense is thus required to rework the superconducting magnet coil support structures.
It would therefore be desirable to provide a method of fabricating a superconducting magnet coil support structure in a MRI system that is more stable, accurate, efficient, and cost reductive relative to the current process used. It would also be desirable for the method to be adaptable for various non-standard geometries and dimensions of the superconducting magnet.